Inter-carrier interference removal device and reception device using the same

ABSTRACT

An inter-carrier interface removal device can improve estimation accuracy of inter-carrier interference caused by Doppler shift in a received multi-carrier signal moving at a high speed, and a reception characteristic of the multi-carrier signal after removing the inter-carrier interference. The inter-carrier interference removal device includes a channel estimation unit estimating a channel frequency characteristic according to a carrier signal, an equalization unit equalizing the carrier signal with the channel frequency characteristic and outputs tentative carrier data, a reliability value calculation unit calculating a reliability value according to the channel frequency characteristic, a weighting unit weighting the tentative carrier data with the reliability value, an ICI component estimation unit estimating an ICI component according to the weighted tentative carrier data and the estimated channel frequency characteristic, and an ICI removal calculation unit removing the ICI component from the carrier signal.

This application is a divisional of U.S. Application Ser. No.12/090,735, filed Apr. 18, 2008, which is a national stage applicationof International Application No. PCT/JP2006/320962, filed Oct. 26, 2006.

TECHNICAL FIELD

In the mobile communication field, the present invention relates to aninter-carrier interference removal device that reduces inter-carrierinterference when a multi-carrier signal is received, and particularlyto a technique to improve a transmission characteristic.

BACKGROUND ART

Currently, Orthogonal Frequency Division Multiplexing (OFDM) has beenwidely used in transmission systems of various digital communicationssuch as digital terrestrial broadcasting and IEEE 802.11a. OFDM, inwhich a plurality of narrowband digital modulation signals arefrequency-multiplexed using multiple orthogonal sub-carriers, is anexcellent transmission system that efficiently utilizes frequencies. Inaddition, in OFDM, each symbol period consists a cycle of a valid symbolperiod and a guard interval. Accordingly, signals in the valid symbolperiod are partially copied into the guard interval, which can reducethe impact of the inter-symbol interference caused by multipathinterference. Thus, OFDM is robust against multipath interference.

However, in OFDM, since one symbol length in a narrowband digitalmodulation signal is longer than that in a broadband digital modulationsignal, OFDM is sensitive to a time variance in a channel fadingenvironment that occurred during the mobile reception and the like.Moreover, in the channel fading environment, in addition to a timevariance in an amplitude of a reception signal that occurs as a resultof delay dispersion due to multipath interference, a frequency variancecalled Doppler shift occurs. This Doppler shift destroys theorthogonality among sub-carriers, and thereby causing mutualinterference among the sub-carriers. Consequently, it is difficult toperform correct demodulation. This interference occurred among thesub-carriers is called inter-carrier interference (ICI). To suppress thedegradation of the communication quality caused by the ICI is the key toimprove the transmission characteristic.

In recent years, several approaches have been made to improve thisdeterioration caused by the ICI. One of the approaches is disclosed inNonpatent Document 3.

FIG. 40 is a block diagram showing the configuration of an ICI removalunit described in Nonpatent Document 3.

A channel characteristic estimation unit 4001 estimates a channelcharacteristic from a signal obtained by FFT (indicated as Y). Atentative equalization unit 4002 divides the post-FFT signal by thechannel characteristic to estimate a transmission signal (indicated asX^(˜)(s), where “s” represents the current symbol number.)

Based on the estimated channel characteristic, a channel characteristiclinear differential calculation unit 4003 calculates, using Expression1, a linear differential (indicated as H′(s)) of a channelcharacteristic H(s) by calculating a difference of the channelcharacteristics between preceding and subsequent symbols of the currentsymbol, and outputs the linear differential H′(s) to a multiplicationunit 4004.

H′(s)=(H(s+1)−H(s−1))/(2·Ts)  (Expression 1)

In Expression 1, the letter “Ts” represents an OFDM symbol length.

Subsequently, the multiplication unit 4004 estimates an ICI componentK(s) with use of Expression 2 by calculating the tentatively equalizedsignal X^(˜)(s), the linear differential H′(s), and a constant matrix Ξ.

K(s)=Ξdiag(H′(s))X ^(˜)(s)  (Expression 2)

The letter, “Ξ” is as expressed in Expressions 3 and 4.

$\begin{matrix}{\Xi = \begin{pmatrix}0 & \zeta_{1} & \ldots & \zeta_{N - 1} \\\zeta_{- 1} & 0 & \ldots & \zeta_{N - 2} \\\vdots & \vdots & \ddots & \vdots \\\zeta_{1 - N} & \zeta_{2 - N} & \ldots & 0\end{pmatrix}} & ( {{Expression}\mspace{14mu} 3} ) \\{\zeta_{n} = {{- \frac{1}{2}} - \frac{j}{2\; {\tan ( {\pi \;/N} )}}}} & ( {{Expression}\mspace{14mu} 4} )\end{matrix}$

In this description, diag(A_(n)(s)) is expressed as a square matrixhaving N lines×N columns as shown below (n=0, . . . , N−1). Note thatthe letter “n” is a carrier number and the letter “N” is the totalcarrier number.

${{diag}( {A_{n}(s)} )} = \begin{pmatrix}{A_{0}(s)} & 0 & \ldots & 0 \\0 & {A_{1}(s)} & \ldots & 0 \\\vdots & \vdots & \ddots & \vdots \\0 & 0 & \ldots & {A_{N - 1}(s)}\end{pmatrix}$

Subsequently, a subtraction unit 1005 performs subtraction to remove,from the post-FFT signal Y, the ICI component estimated from Expression2.

-   Nonpatent Document 1: ARIB STD-B31-   Nonpatent Document 2: IEEE Std 802.11a-1999-   Nonpatent Document 3: Karsten Schmidt et al, “Low Complexity    Inter-Carrier Interference Compensation for Mobile Reception of    DVB-H,” 9^(th) International OFDM-Workshop 2004, Dresden (Page    72-76, FIG. 4)-   Patent Document 1: JP Patent Publication No. 2004-519900

DISCLOSURE OF THE INVENTION Problems the Invention is Attempting toSolve

However, the inter-carrier interference removal device disclosed inNonpatent Document 3 has the following problem. In a multipath fadingenvironment, a channel characteristic exhibits frequency selectiveness,and dips are caused in a reception band. Levels of some carriers arelower than other carriers and many noise components are contained. Insuch a case, or when interferences are contained in particular carriers,errors can be occurred in estimating, with use of such carriers,tentative carrier data and a channel variation, which results inerroneous calculation of an interference component that interferes othercarriers.

When there is a serious error in the estimation of the tentative carrierdata in the carrier, the error causes an increase in inter-carrierinterference, far from removing the inter-carrier interference.

In view of the above problems, the object of the present invention is toprovide an inter-carrier interference removal device that is able toaccurately estimate and remove an ICI component when the channelcharacteristic shows frequency selectiveness or when interferences arecontained in the multipath fading environment.

Means for Solving the Problems

In order to solve the aforementioned problems, the present inventionprovides an inter-carrier interference removal device that removes aninter-carrier interference component from a multi-carrier signal, themulti-carrier signal including a plurality of carrier signals eachindicating a frequency response characteristic that varies with achannel status, the inter-carrier interference removal device includingan acquisition unit operable to acquire a multi-carrier signal includinga plurality of carrier signals; a reliability value calculation unitoperable to calculate a reliability value of each carrier signal basedon a frequency response characteristic of the carrier signal; anequalization unit operable to equalize each carrier signal; a weightingunit operable to weight each equalized carrier signal with use of thereliability value of each non-equalized carrier signal; and aninter-carrier interference removal unit operable to (i) calculate, foreach carrier signal, an inter-carrier interference component based on avariation of the frequency response characteristic of the non-equalizedcarrier signal, and the weighted and equalized carrier signal, and (ii)remove the inter-carrier interference component from the non-equalizedcarrier signal.

Effects of the Invention

With the above configuration, the inter-carrier interference removaldevice of the present invention weights a carrier signal with thereliability value based on the frequency response characteristic, andsubsequently calculates an inter-carrier interference component.Therefore, in a reception environment where an influence of themultipath shows frequency selectivity when a multi-carrier signal isreceived, and where inter-carrier interference occurs as a result of ahigh-speed variance of a radio channel, the inter-carrier interferenceremoval device is ensured to estimate and remove an inter-carrierinterference component generated in a carrier signal more accuratelythan conventionally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the configuration of an OFDM receptiondevice that includes an inter-carrier interference removal device inaccordance with Embodiment 1 of the present invention;

FIG. 2 is a block diagram of the inter-carrier interference removaldevice of Embodiment 1;

FIG. 3 shows a signal format of an OFDM signal disclosed in NonpatentDocument 1;

FIG. 4 is a block diagram of a channel variation estimation unit of theinter-carrier interference removal device of Embodiment 1;

FIG. 5 is a block diagram of an ICI removal operation unit of theinter-carrier interference removal device of Embodiment 1;

FIG. 6 is a schematic view showing frequency selectiveness of a carriersignal;

FIG. 7 is a diagram showing a characteristic when a linear function isemployed as an example of the function f(x);

FIG. 8 schematically shows a carrier that is weighted with a reliabilityvalue when the linear function is employed as an example of the functionf(x);

FIG. 9 is a diagram showing a characteristic when a step function isemployed as an example of the function f(x);

FIG. 10 schematically shows a carrier that is weighted with areliability value when the step function is employed as the functionf(x);

FIG. 11 is a diagram showing a characteristic when the function f(x) isthe linear function and an input is normalized by an average amplitude;

FIG. 12 schematically shows that a carrier signal is weighted by alinear function when the average amplitude of a carrier is used as thereference;

FIG. 13 schematically shows average power that is normalized by anaverage of a plurality of carriers;

FIG. 14 is a schematic view of carriers of a TMCC signal and an ACsignal in ISDB-T;

FIG. 15 is a block diagram of an inter-carrier interference removalsystem disclosed in Nonpatent Document to which a reliability valuecalculation unit and a weighting unit of the present invention areapplied;

FIG. 16 is a block diagram of an inter-carrier interference removaldevice disclosed in Patent Document 1 to which the reliability valuecalculation unit and the weighting unit of the present invention areapplied;

FIG. 17 is a block diagram of an inter-carrier interference removaldevice in accordance with Embodiment 2 of the present invention;

FIG. 18 is a detailed block diagram of an inter-carrier interferenceremoval device in accordance with Embodiment 3 of the present invention;

FIG. 19 is a block diagram of a reliability value calculation unit in aninter-carrier interference removal device in accordance with Embodiment4 of the present invention;

FIG. 20 is a block diagram of an interference judgment unit in theinter-carrier interference removal device of Embodiment 4;

FIG. 21 is a block diagram of a diversity reception device to which theinter-carrier interference removal device of the present invention isapplied;

FIG. 22 is a block diagram of a demodulation unit for diversityreception that includes in an inter-carrier interference removal devicein accordance with Embodiment 5 of the present invention;

FIG. 23 is a block diagram of an inter-carrier interference removaldevice in accordance with Embodiment 6 of the present invention;

FIG. 24 is a schematic view showing a distance between a signal point oftentative carrier data of each branch and a signal point of combinedcarrier data;

FIG. 25 is a schematic view showing, when there are four branches, adistance between a signal point of tentative carrier data and a signalpoint of combined carrier data;

FIG. 26 is a block diagram of an inter-carrier interference removaldevice in accordance with Embodiment 7 of the present invention;

FIG. 27 is a block diagram of an inter-carrier interference removaldevice that includes a block that performs a clip processing ontentative carrier data;

FIG. 28 is a view schematically showing amplitudes that the clipprocessing unit 2401 clips;

FIG. 29 is a block diagram of a reception device in accordance withEmbodiment 9 of the present invention;

FIG. 30 is a block diagram of a reception processing unit of FIG. 29;

FIG. 31 is a block diagram of a demodulation unit of FIG. 30;

FIG. 32 is a block diagram of a channel characteristic estimation unitof FIG. 31;

FIG. 33 is a block diagram of an ICI component generation unit of FIG.31;

FIG. 34 is a block diagram of the reception device of Embodiment 1 thatperforms diversity combining in three steps;

FIG. 35 is a block diagram of a reception processing unit of FIG. 34;

FIG. 36 is a block diagram of a demodulation unit of FIG. 35;

FIG. 37 is a block diagram of a reception device in accordance withEmbodiment 10 of the present invention;

FIG. 38 is a block diagram of a reception processing unit of FIG. 37;

FIG. 39 is a block diagram of a demodulation unit of FIG. 38;

FIG. 40 is a block diagram of the ICI removal unit of Nonpatent Document3; and

FIG. 41 schematically shows an OFDM symbol.

REFERENCE NUMERALS

-   1 inter-carrier interference removal device-   101 channel estimation unit-   102 equalization unit-   103 reliability value calculation unit-   104 weighting unit-   105 channel variation estimation unit-   106 ICI component estimation unit-   107 ICI removal operation unit-   110 carrier signal-   111 channel frequency characteristic-   112 tentative carrier data-   113 reliability value-   114 weighted tentative carrier data-   115 channel variation characteristic-   116 ICI component-   117 carrier signal from which ICI component has been removed-   201 transmitter station-   202 mobile reception station-   501 channel estimation unit-   502 equalization unit-   503 channel variation estimation unit-   504 ICI component estimation unit-   505, 506, 507 symbol delay unit-   508 subtraction unit-   510 carrier signal    -   511 channel frequency characteristic    -   514 tentative carrier data    -   515 channel variation characteristic    -   516 ICI component-   517 carrier signal from which ICI component has been removed-   702 RF unit-   703 A/D unit-   704 symbol synchronization unit-   705 guard removal unit-   706 frequency domain conversion unit-   707 ICI removal unit-   708 channel estimation unit-   709 equalization unit-   710 decode unit-   720 baseband signal-   726 channel frequency characteristic-   727 carrier data-   901 channel variation calculation unit-   902, 903 symbol delay unit-   1000 subtraction circuit

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes embodiments of the present invention, withreference to the attached drawings. Note that the below descriptions aregiven by way of example of a device whose multi-carrier modulationsystem is OFDM system, and whose signal format is ISDB-T system asdisclosed in Nonpatent Document 1.

Embodiment 1

A reception device in accordance with Embodiment 1 of the presentinvention includes an inter-carrier interference removal device. Theinter-carrier interference removal device calculates a reliability valueof a carrier signal based on a channel frequency characteristic of acarrier, and estimates an ICI component more accurately with use of thereliability value. Thus, the reception device is able to accuratelyremove the ICI component from the carrier signal, and therefore thereception performance at a high-speed OFDM mobile communication isimproved.

The following describes a reception device 1 in accordance withEmbodiment 1 of the present invention, with reference to the attacheddrawings.

<Configuration>

As shown in FIG. 1, the reception device 1 includes: an RF unit 702 thatreceives a wave of a desired channel via an antenna 701 and converts anRF (Radio Frequency) signal to a baseband signal 720; an A/D unit 703that converts an analogue signal to a digital signal; a symbolsynchronization unit that performs synchronization processing on an OFDMsymbol; a guard removal unit 705 that remove a guard interval containedin the OFDM symbol; a frequency domain conversion unit 706 that convertsa time domain OFDM signal to a frequency domain carrier signal 110; anICI removal unit 707 that estimates and removes an ICI component fromthe carrier signal 110; a channel estimation unit 708 that estimates afrequency response characteristic of a channel from a carrier signal 117from which the ICI component has been removed, and outputs a channelfrequency characteristic 726; an equalization unit 709 that equalizesthe carrier signal 110 based on the channel frequency characteristic726, and outputs carrier data 727; and a decode unit 710 that performserror correction on the carrier data 727 and acquires a reception bitdata 728.

The reception device 1, in concrete, is composed of an antenna, a tuner,a decoder LSI, and the like.

In this embodiment, the FFT (Fast The Fourier transform) is employed byway of example of converting a time domain signal to a frequency domainsignal in the frequency domain conversion unit 706. Since units otherthan the ICI removal unit 707 are publicly known as units included in areception device that demodulates an OFDM signal, operations of theseunits are not described in detail.

Subsequently, the inter-carrier interference removal device 707 that isequivalent to the ICI removal unit 707 is described, with reference toFIG. 2.

FIG. 2 is a detailed block diagram of the inter-carrier interferenceremoval device 707.

As shown in FIG. 2, the inter-carrier interference removal device 707includes a channel estimation unit 101, an equalization unit 102, areliability value calculation unit 103, a weighting unit 104, a channelvariation estimation unit 105, an ICI component estimation unit 106, andan ICI removal operation unit 107.

The channel estimation unit 101 estimates a frequency responsecharacteristic of a channel from the carrier signal 110, and outputs achannel frequency characteristic 111. In the ISDB-T system, the channelestimation unit 101 estimates the frequency response characteristic withuse of a pilot carrier contained in the carrier signal 110.

The following describes the estimation of the frequency responsecharacteristic, with reference to the drawings.

FIG. 41 is a schematic view of an OFDM symbol. In the followingdescription, each length of the OFDM symbol is expressed as follows. Thesymbol length is T_(s), the guard length is T_(g), and the valid symbollength is T_(u).

FIG. 3 shows a format of an OFDM signal. The outline circles in thefigure represent data carriers, and the black circles in the figurerepresent pilot carriers. The letter “s” in the figure represents asymbol number. Since carrier data X_(p) (P is a carrier number of apilot carrier) is known to a receiving side, with use of the carrierdata X_(p), a channel frequency characteristic H_(p) of a pilot carrieris obtained by equalizing, by a division expressed in Expression 5,carrier data Y_(p) that is actually received.

H _(p) =Y _(p) /X _(p)  (Expression 5)

The channel frequency characteristics of the data carriers between pilotcarriers are calculated by interpolating the neighboring OFDM symbolsH_(p) (in the symbol direction). For example, the channel frequencycharacteristic of a pilot carrier 151 is supposed to be H_(n)(s−4), thechannel frequency characteristic of a pilot carrier 152 is supposed tobe H_(n)(s). The channel frequency characteristics of the data carriers153, 154 and 155 are supposed to be H_(n)(s−1), H_(n)(s−2) andH_(n)(s−3), respectively. In this case, H_(n)(s−1), H_(n)(s−2) andH_(n)(s−3) can be obtained by interpolating between H_(n)(s−4) andH_(n)(s).

In addition, the channel frequency characteristics of the total carriersincluding the data carriers are estimated, for every symbol, byinterpolating the frequency response characteristics of every fourcarrier in the carrier direction.

For example, the channel frequency characteristics H_(n+1)(s) of a datacarrier 157 and the channel frequency characteristic H_(n+2)(s) of adata carrier 158 are obtained by interpolating, in the carrierdirection, between a channel frequency characteristic H_(n+3)(s) of adata carrier 156 and the channel frequency characteristic H_(n)(s) ofthe pilot carrier 152. The channel frequency characteristic H_(n+3)(s)is obtained by interpolation in the symbol direction.

The equalization unit 102 equalizes, by a division expressed inExpression 6, the carrier signal Y(s) based on the channel frequencycharacteristic H(s), and estimates tentative carrier data X^(˜)(s).

X ^(˜)(s)=Y(s)/H(s)  (Expression 6)

Based on the channel frequency characteristic H (s), the channelvariation estimation unit 105 calculates a variation H′(s) of thechannel frequency characteristic (hereinafter, referred to as a channelvariation characteristic) occurred in the preceding and subsequentsymbols to the symbol s from which ICI is to be removed.

As shown in FIG. 4, the channel variation estimation unit 105 includessymbol delay units 902 and 903 that delay for the OFDM symbol lengthT_(s), and a channel variation calculation unit 901. The channelvariation estimation unit 105 estimates the channel variationcharacteristic H′_(n)(s) of the s-th symbol, with use of the channelfrequency characteristic H_(n)(s+1) of an input carrier n and H_(n)(s−1)that is delayed by those two symbol delay units, by performing operationbased on Expression 7 in the channel variation calculation unit 901.

H′ _(n)(s)=(H _(n)(s+1)−H _(n)(s−1))/(2·Ts)  (Expression 7)

The reliability value calculation unit 103 calculates reliability valueW(s) of the tentative carrier data X^(˜)(s). For each carrier,reliability value W_(n)(s) of a carrier n is calculated based on thechannel frequency characteristic H_(n)(s), and the relation isassociated with a given function f (·) (Expression 8) that is describedlater. The “abs[z]” indicates an amplitude of a vector z.

W _(n)(s)=f(abs[H _(n)(s)])  (Expression 8)

-   -   (n=0, . . . , N−1, Note≠m)

The weighting unit 104 weights the weight W_(n)(s) calculated by thereliability value calculation unit 103 by multiplying the weightW_(n)(s) and the tentative data symbol X^(˜) _(n)(s) together.

X̂ _(n)(s)=X ^(˜) _(n)(s)·W _(n)(s)  (Expression 9)

-   -   (n=0, . . . , N−1, Note≠m)

As shown in Expression 10, the ICI component estimation unit 106estimates the ICI component K(s) by multiplying the leak matrix E, thechannel variation characteristic H′(s) and the weighted tentativecarrier data X̂(s).

$\begin{matrix}\begin{matrix}{{K(s)} = {\Xi \cdot {H^{\prime}(s)} \cdot {W(s)} \cdot {X^{\sim}(s)}}} \\{= {\Xi \cdot {H^{\prime}(s)} \cdot {X^{\hat{}}(s)}}}\end{matrix} & ( {{Expression}\mspace{14mu} 10} )\end{matrix}$

Herein, the letters, K(s), Ξ, H′(s), W(s) and X^(˜)(s) are respectivelyexpressed in matrices shown in Expressions 11-15. Herein, the letter,“^(T)” represents a transposition.

K(s)=[K ₁(s),K ₂(s),K _(N−1)(s)]^(T)  (Expression 11)

$\begin{matrix}{\Xi = \begin{pmatrix}0 & \zeta_{1} & \ldots & \zeta_{N - 1} \\\zeta_{- 1} & 0 & \ldots & \zeta_{N - 2} \\\vdots & \vdots & \ddots & \vdots \\\zeta_{1 - N} & \zeta_{2 - N} & \ldots & 0\end{pmatrix}} & ( {{Expression}\mspace{14mu} 3} ) \\{\zeta_{n} = {{- \frac{1}{2}} - \frac{j}{2\; {\tan ( {\pi \;/N} )}}}} & ( {{Expression}\mspace{14mu} 4} )\end{matrix}$H′(s)=diag(H′ _(n)(s))  (Expression 12)

W(s)=diag(W _(n)(s))  (Expression 13)

X ¹⁸(s)=[X ^(˜) ₁(S),X ^(˜) ₂(S), . . . ,X ^(˜)_(N−1)(s)]^(T)  (Expression 14)

As shown in Expression 15, the ICI removal operation unit 107 removesthe ICI component by subtracting an estimated ICI component K_(n)(s)from an input carrier signal Y_(n)(s).

Y ^(˜)(s)=Y(s)−K(s)  (Expression 15)

As shown in FIG. 5, the ICI removal operation unit 107 is implemented ina subtraction circuit 1000.

Described as above, the inter-carrier interference removal device ofEmbodiment 1 is characterized by having the reliability valuecalculation unit that calculates the reliability value based on thechannel frequency characteristic and the weighting unit.

<Operation>

The following is a detailed description of an operation of theinter-carrier interference removal device 707.

Initially, the inter-carrier interference removal device 707 estimatestentative carrier data that is necessary for estimating an ICIcomponent. For that purpose, the channel estimation unit 101 estimates achannel frequency characteristic H(s), and the equalization unit 102equalizes the carrier signal Y(s) with use of the H(s). Thus, thetentative data symbol X^(˜)(s) is obtained. For channel estimation,pilot carriers that are known to a receiving side, as shown in FIG. 3,are used. Depending on an amount of delay of multipath and phaserelation between paths, as shown in FIG. 6A, levels of carriers arerelatively different from one another, and particular carriers (e.g. acarrier 161 and a carrier 162) have low carrier levels.

FIG. 6 schematically shows frequency selectiveness of a carrier signal.

As for the channel frequency characteristic H_(n)(s) of the n-thcarrier, the abs[H_(n)(s)] represents an amplitude of each carriersignal. When the amplitude of H_(n)(s) is small, the amplitudeapproximates to a noise level. Therefore, the equalization by Expression6 results in a higher risk of erroneous estimation of the tentative datasymbol X^(˜) _(n)(s). As a result, estimation of interference to othercarriers may be erroneous. Furthermore, calculation of an interferingamount (leak amount) with use of the erroneous carrier data adverselygenerates ICI. Accordingly, when the estimation of carrier data can bewrong, which means the carrier data has a low reliability value,reducing the use of such carrier data to estimate an ICI componentimproves the accuracy of the estimation.

Accordingly, in the present invention, the tentative carrier data X̂(s)that is necessary for estimating an ICI component is weighted accordingto a reliability value of a carrier, and thus the reliability value ofthe estimation of the ICI component is improved.

More specifically, the reliability value calculation unit 103 calculatesthe reliability value W_(n)(s) of the tentative data symbol X̂_(n)(s)based on the channel frequency characteristic H_(n)(s).

Thus, the reliability value W_(n)(s) of a carrier n is expressed as afunction f(x) whose input x is abs[H_(n)(s)] as shown in Expression 16.

W _(n)(s)=f(abs[H _(n)(s)])  (Expression 16)

The detail of the function f(x) is described later.

Subsequently, the weighting unit 104 multiplies the tentative datasymbol X^(˜) _(n)(s) by the reliability value W_(n)(s).

The channel variation estimation unit 105 calculates the channelvariation H′(s) with use of channel frequency characteristics H(s+1) andH(s−1) that are in the vicinity of the s-th OFDM symbol from which anICI component is to be removed. The ICI component estimation unit 106estimates the ICI component K(s) with use of the operation shown inExpression 10.

Subsequently, the ICI removal operation unit 107 removes the estimatedICI component K_(n)(s) by subtracting the ICI component K_(n)(s) fromthe carrier signal Y^(˜) _(n)(s).

The channel estimation unit 708 and the equalization unit 709 that aresubsequent to the ICI removal operation unit 707 respectively performchannel estimation on the carrier signal Y^(˜), (s) from which the ICIcomponent has been removed, and equalization processing based on thechannel estimation. After error correction, the decode unit 710 obtainsreception bit data.

The following describes the function f(x) and its input x employed bythe reliability value calculation unit 103. The following firstdescription is when the input x is abs[H_(n)].

The function f(x) can be a function shown in Expression 17, for example.Note that α>1. The α may be set to a value appropriate for a system.

$\begin{matrix}\begin{matrix}{{f(x)} = {0\mspace{140mu} ( {0 \leq x < {( {\alpha - 1} )/\alpha}} )}} \\{= {{\alpha ( {x - 1} )} + {1\mspace{25mu} ( {{( {\alpha - 1} )/\alpha} \leq x \leq 1} )}}} \\{= {1\mspace{140mu} ( {1 < x} )}}\end{matrix} & ( {{Expression}\mspace{14mu} 17} )\end{matrix}$

Suppose the amplitude of a pilot carrier is 1, and is set to be thereference, according to Expression 5, the abs[H_(n)]=1 can also be thereference. Thus, x=abs[H_(n)]. Expression 17 shows that when theamplitude abs[H_(n)] of a carrier signal ranges from (α−1)/α to 1, thereliability value is related by a linear function that is proportionalto the amplitude of the carrier signal. When the abs[H_(n)] is smallerthan (α−1)/α, the reliability value is zero (See FIG. 7).

The zero reliability value means that the interfering of the carrier nto the carrier m is not counted.

FIG. 7 shows the characteristic of a linear function that is employed asan example of the function f(x).

FIG. 8 schematically shows a carrier that is weighted with thereliability value when the linear function is employed as an example ofthe function f(x).

As for carriers 171 and 172 whose f(x) value ranges between 0-((α−1)/α),the reliability value is zero.

The following description is when the f(x) is a step function as shownin Expression 18.

$\begin{matrix}\begin{matrix}{{f(x)} = {0\mspace{14mu} ( {0 \leq x < a} )}} \\{= {1\mspace{14mu} ( {a \leq x} )}}\end{matrix} & ( {{Expression}\mspace{14mu} 18} )\end{matrix}$

For example, in a case of a step function that leads the zeroreliability value in a range of x<a, when the amplitude of the carrieris smaller than the given threshold a, the estimated value of tentativecarrier data of the carrier is assumed to have a low reliability value,and no interfering is counted.

FIG. 9 shows the characteristic of a carrier when the step function isemployed as an example of the function f(x).

FIG. 10 schematically shows a carrier signal weighed with thereliability value when the step function is employed as the functionf(x).

For example, as for a carrier 181, when its value of the f(x) is 0-a,its reliability value is zero.

In addition, the reference input of the function f(x) may be an averageof amplitudes of carriers.

FIG. 11 shows the characteristic of a carrier when the function f(x) isthe linear function and an input is normalized by an average ofamplitudes.

FIG. 12 schematically shows that a carrier signal is weighted by alinear function when the average of amplitudes of carriers is used asthe reference. To calculate the average of amplitudes, calculation withuse of all carriers (carrier 0 to carrier (N−1)) (Expression 19) andcalculation with use of only a plurality of carriers in the vicinity ofthe carrier n (carrier (n−L) to carrier (n+L)) (Expression

20) can be used.

$\begin{matrix}{x = {{{abs}( H_{n} )}/{\sum\limits_{k = 0}^{N - 1}\; {{abs}( H_{k} )}}}} & ( {{Expression}\mspace{14mu} 19} ) \\{x = {{{abs}( H_{n} )}/{\sum\limits_{k = {n - L}}^{n + L}\; {{abs}( H_{k} )}}}} & ( {{Expression}\mspace{14mu} 20} )\end{matrix}$

Note that, in Expression 20, the average of n=L is substituted for (n=0,1, . . . L−1). Similarly, the average of n=N−L−1 is substituted for(n=N−L, N−L+1, . . . ,N−1). Note that the f(x) is an integer in a rangeof 1<L<N−2.

Also, the input reference of the function f(x) may be average power ofcarriers.

FIG. 13 schematically shows average power when average power isnormalized by an average of a plurality of carriers.

In FIG. 13, when the reference input of the function f(x) is determinedby the reliability value of a carrier A, the reliability value can bedetermined with use of a value normalized by average power calculatedfrom a plurality of carriers in the vicinity of the carrier A.Similarly, when the reference input of the function f(x) is determinedby the reliability value of a carrier B, the reliability value can bedetermined with use of a value normalized by average power calculatedfrom a plurality of carriers in the vicinity of the carrier B. Thus, thereliability value can be determined by a value normalized by averagepower calculated with use of carriers in the vicinity of the carrier n.

In FIG. 13, the reliability value of each carrier 191 and 192 is zero.

Thus, determining the reliability value with use of the value normalizedby the average power calculated in the vicinity of the carrier n causesa change in the threshold that makes the reliability value zero. Sincethe closer carriers suffer more from interference than the distantcarriers, using the average power calculated in the vicinity of thecarrier as the reference is better for accurately showing the relativityamong carrier levels. Thus, the reliability value of each carrier ismore accurately determined.

The input x of the function f (x) may be a square (power) of anamplitude of a carrier. In this case, the input x is as expressed inExpression 21.

x=abs[H _(n) ]·abs[H _(n)]  (Expression 21)

Also, the input x may be a square (power) of the amplitude of thecarrier n normalized by the average of the carriers in the vicinity ofthe carrier n.

The calculation of the average power may be performed with use of allcarriers (carrier 0 to carrier (N−1)) (Expression 22) and with use ofonly the carrier n and the carriers in its vicinity (carrier (n−L) tocarrier (n+L) (Expression 23).

$\begin{matrix}{x = {( {{{abs}( H_{n} )} \cdot {{abs}( H_{n} )}} )/{\sum\limits_{k = 0}^{N - 1}\; ( {{{abs}( H_{k} )} \cdot {{abs}( H_{k} )}} )}}} & ( {{Expression}\mspace{14mu} 22} ) \\{x = {( {{{abs}( H_{n} )} \cdot {{abs}( H_{n} )}} )/{\sum\limits_{k = {n - L}}^{n + L}\; ( {{{abs}( H_{k} )} \cdot {{abs}( H_{k} )}} )}}} & ( {{Expression}\mspace{14mu} 23} )\end{matrix}$

Note that in Expression 23, when (n=0, 1, . . . ,L−1), the average ofn=L is substituted. Similarly, when (n=N−L, N−L+1, . . . ,N−1), theaverage of n=N−L−1 is substituted. Note that the f (x) is an integer ina range of 2≦L≦N−2.

In addition, as shown in Expression 24, the input x may be a logarithmof the above input x.

$\begin{matrix}{x = {{10 \cdot \log_{10}}\{ {( {{{abs}( H_{n} )} \cdot {{abs}( H_{n} )}} )/{\sum\limits_{k = 0}^{N - 1}\; ( {{{abs}( H_{k} )} \cdot {{abs}( H_{k} )}} )}} \}}} & ( {{Expression}\mspace{14mu} 24} )\end{matrix}$

For example, Expression 24 is a logarithm of Expression 22.

The above is the description of the input x of the function f (x) whenthe input x is the amplitude of the carrier, the square (power) of theamplitude, and the square of the amplitude normalized by the average ofthe plurality of carriers.

As an example of the function f (x), the above also describes that thefunction f(x) that is expressed in the linear function (Expression 17)or is expressed in the step function that becomes 0 or 1 when theamplitude reaches the given threshold (Expression 18). However, thefunction f(x) is not limited to those as long as the reliability valueof a carrier can effectively contribute to the calculation of an ICIcomponent.

Thus, since the inter-carrier interference removal device of Embodiment1 calculates the reliability value based on the reliability value of thecarrier (Expression 8) and calculates the ICI component with use of thereliability value (Expression 10), the reliability in estimating the ICIcomponent can be enhanced.

Accordingly, the present invention is able to remove an ICI componentmore accurately, and consequently improve the reception performance ofthe reception device that moves at a high speed in OFDM system.

Note that as for carriers of pilot carriers, since their carrier data isknown to a receiving side, an interfering component can be moreaccurately estimated than data carriers. Accordingly, since the pilotcarriers can be assumed to possess high reliability values, it isdesirable not to weight the pilot carriers.

Furthermore, in ISDB-T, particular carriers are allocated to controlinformation such as a TMCC (Transmission Multiplexing ConfigurationControl) signal and an AC (Auxiliary Channel) signal. The TMCC signalmainly transmits transmission parameters such as a modulation scheme andan encoding ratio, and the AC signal transmits additional information.

FIG. 14 schematically shows carriers of the TMCC signal and the ACsignal in the ISDB-T system.

In the TMCC signal and the AC signal, since differential BPSK is used asprimary modulation, the error rate is remarkably lower than datacarriers that use 64QAM as the primary modulation. Therefore, in thecarriers of the TMCC signal and the AC signal, an ICI component can beestimated with use of the reliable carrier data. Thus, since thecarriers of the TMCC signal and the AC signal can be assumed to bereliable, and it is desirable not to weight the carriers of the TMCCsignal and the AC signal.

Accordingly, suppose a carrier number of a pilot carrier is p, and acarrier number of each of the TMCC signal and the AC signal is t, whenn=p, t, the reliability value W_(n)(s) is as expressed in Expression 25.

W _(n)(s)=1(n=p,t)  (Expression 25)

Note that in the multiplication of the W (s) in Expression 10, modifiedExpression 26 shows the same operation result.

K(s)=Ξ·W(s)·H′(s)·X ^(˜)(s)  (Expression 26)

Accordingly, in the operational process to estimate an ICI component, amultiplication process, where the W(s) is multiplied by a circuit blockthat estimates the ICI component, is not essential, and other processthat has the same estimation result may be used.

In the channel variation estimation unit, to obtain the channelvariation characteristic of the symbol s, the channel variationcharacteristic H′(s) of the symbol s is estimated from a symbol s+1 anda symbol s−1 that are adjacent to the symbol s. A symbol s+2 and asymbol s−2 can be also used to determine the channel variationcharacteristic of the symbol s. Note that the estimation does not dependon the symbol number.

Note that when the reliability value calculation unit and the weightingunit of the present invention are applied to the inter-carrierinterference removal system disclosed in Nonpatent Document 3, itsprocessing block diagram is as shown in FIG. 15.

FIG. 15 is a block diagram of the inter-carrier interference removalsystem disclosed in Nonpatent Document 3 to which the reliability valuecalculation unit and the weighting unit of the present invention areapplied.

According to the processing to which the reliability value calculationunit and the weighting unit are added as shown in FIG. 15, aninter-carrier interference component generated in a carrier is moreaccurately estimated and removed, which can improve the receptioncharacteristic.

Embodiment 2

Embodiment 1 describes a case where the present invention is applied tothe ICI removal system that performs feedforward processing in whichtentative symbol data is estimated, and equalization is performed againafter removal of the ICI component. On the other hand, Embodiment 2shows a case where the present invention is applied to the ICI removalsystem that performs feedback processing.

In specific, an inter-carrier interference removal device in accordancewith Embodiment 2 calculates a reliability value based on a channelfrequency characteristic estimated by the reliability value calculationunit, and weights the estimated carrier data with the reliability value.Thus, the reliability value of the estimation of the ICI component isenhanced, and carrier data can be reliably estimated by removing an ICIcomponent more accurately. As a result, the reception performance at ahigh-speed travel in OFDM system can be improved.

The following describes an inter-carrier interference removal device1200 in accordance with Embodiment 2 with reference to the attacheddrawings.

As shown in FIG. 16, the inter-carrier interference removal device 1200is composed of a subtraction unit 1102, a channel estimation unit 1103,an equalization unit 1104, a multiplication unit 1105, a leak matrixmultiplication unit 1106, a reliability value calculation unit 1201 anda weighting unit 1202.

Concretely, the inter-carrier interference removal device 1200 isimplemented in an LSI.

The subtraction unit 1102 obtains a carrier signal that has beenconverted from a time domain signal to a frequency domain signal by anFFT unit that is an exterior unit of the inter-carrier interferenceremoval device. The subtraction unit 1102 removes an estimated ICIcomponent from the carrier signal by a subtraction.

The channel estimation unit 1103 estimates a channel frequencycharacteristic H and a time derivative d̂ (namely, a time variation of achannel).

The equalization unit 1104 equalizes a carrier signal 1113 with use ofthe channel frequency characteristic H and outputs carrier data ŝ 1115.

Based on a channel frequency characteristic 1114 estimated by thechannel estimation unit 1103, the reliability value calculation unit1201 calculates a reliability value 1210 of a carrier according toExpression 27.

W _(n)(s)=f(abs[H _(n)(s)])  (Expression 27)

With use of W_(n), the weighting unit 1202 weights estimated carrierdata ŝ_(n) of each carrier.

The multiplication unit 1105 multiplies the time derivative d̂ 1116 andthe carrier data weighted by the weighting unit 1202 together. The leakmatrix multiplication unit 1106 further multiplies a multiplicationresult by the leak matrix Ξ, and estimates an ICI component 1118.

The feedback processing repeats the above operational processing formultiple times, which improves the estimation accuracy of an ICIcomponent.

Expression 28 shows the feedback processing mathematically. Theoperation shown in Expression 28 enables the accurate estimation of thecarrier data.

Y(i)=Y−Ξ·(d̂(i−1)·ŝ(i−1)·diag(W _(n)(s)))  (Expression 28)

Herein, the “i” shows the number of the operational processing.

Note that the output from the inter-carrier interference removal device1200 is the carrier data, and that the inter-carrier interferenceremoval device 1200 is equivalent to the ICI removal unit 707 in FIG.17. As shown in FIG. 17, the subsequent stage to the ICI removal unit707 is not a channel estimation unit or equalization unit but the decodeunit 710.

As described above, since the inter-carrier interference removal device1200 of Embodiment 2 calculates the reliability value 1210 based on thechannel frequency characteristic 1114 estimated by the reliability valuecalculation unit 1201, and weights the estimated value of the carrierdata 1115 with the reliability value 1210, the ICI component can be morereliably estimated.

Accordingly, the inter-carrier interference removal device 1200 removesan ICI component and estimates carrier data more accurately, whichresults in improvement in the reception performance at a high-speed movein OFDM system.

As described in Embodiments 1 and 2, the present invention weights theadjacent carriers based on the reliability value of the carrier, andestimates an ICI component. The present invention focuses attention ondependency of an ICI component on carrier data of neighboring carriers.The present invention can be applied to any system to estimate an ICIcomponent, the leak from the adjacent carriers being considered. Adetailed ICI removal method or circuit configuration of the ICI removalis not essential.

Embodiment 3

In Embodiments 1 and 2, a description is made on a case in which anestimated ICI component is removed by being subtracted from a receivedcarrier signal. Embodiment 3 describes a case where the presentinvention is applied to a calculation, with use of an inverse matrixoperation, of carrier data from which an ICI component has been directlyremoved.

First, the processing performed in Embodiment 3 is described with use ofexpressions. Subsequently, the configuration and the operation of theEmbodiment 3 are described.

As one of the formula to estimate an ICI component (Expression 10),Expression 29 shows a case in which weighting is not performed with useof the reliability value.

K(s)=Ξ·H′(s)·X ^(˜)(s)  (Expression 29)

A carrier signal from which an ICI component has been removed can beexpressed as Y(s)=H(s)·X(s). Accordingly, in Expression 29, carrier datais supposed to be carrier data X^(˜). When X^(˜)(s)=X(s), relationalexpression as shown in Expression 30 can be obtained from Expression 15.

H(s)·X(s)=Y ^(˜)(s)−Ξ·H′(s)·X(s)  (Expression 30)

is modified to

H(s)·X(s)+Ξ·H′(s)·X(s)=Y ^(˜)(s)  (Expression 31)

is further modified to obtain

X(s)=(H(s)+Ξ·H′(s))⁻¹ ·Y ^(˜)(s)  (Expression 32)

Herein, (·)⁻¹ shows the inverse matrix operation.

Accordingly, multiplying the inverse matrix of (H(s)+Ξ·H′(s)) with areceived carrier signal Y^(˜)(s) directly results carrier data X (s)from which an ICI component has been removed. (H(s)+Ξ·H′(s)) is supposedto be the channel frequency characteristic that includes inter-carrierinterference.

In Expression 32, H(s) and H′(s) are variables to be estimated. SinceH′(s) is calculated from Expression 7, the estimation value of thereliability value is determined according to a carrier level.

Therefore, similarly to Embodiment 1, the reliability value W_(n)(s)that is determined based on the H_(n)(s) is defined as shown inExpression 33. When H′(s) is weighted according to the reliability valueof each carrier, the channel frequency characteristic includinginter-carrier interference can be calculated accurately.

W _(n)(s)=f(abs[H _(n)(s)])  (Expression 33)

Accordingly,

X(s)=(H(s)+Ξ·H′(s)·diag(W _(n)(s)))⁻¹ ·Y ^(˜)(s)  (Expression 34)

Thus, the operation shown in Expression 34 enables accurate estimationof carrier data.

Below is a description of an inter-carrier interference removal device1400 in accordance with Embodiment 3 that estimates carrier data basedon Expression 34.

As shown in FIG. 18, the inter-carrier interference removal device 1400is composed of a channel estimation unit 101, a reliability valuecalculation unit 103, a channel variation estimation unit 105, a channelICI characteristic estimation unit 1401, an inverse matrix operationunit 1402, a channel ICI inverse characteristic multiplication unit 1403and a weighting unit 1404.

The configuration units that are basically identical with those thathave been already described have identical reference numbers.Description of such configuration units is omitted unless necessary.

The weighting unit 1404 weights the H′_(n)(s) estimated by the channelvariation estimation unit 105 by multiplying with the reliability valueW_(n)(s) calculated by the reliability value calculation unit 103. Theweighting unit 1404 outputs a multiplication result that is the channelvariation characteristic 1410.

As shown in Expression 35, the channel ICI characteristic estimationunit 1401 estimates a channel ICI characteristic K′(s) that includesmutual interference characteristic of ICI with use of the channelcharacteristic H(s) and the channel variation characteristicH′(s)·diag(W_(n)(s)) weighted by the leak matrix Ξ.

K′(s)=H(s)+Ξ·H′(s)·diag(W _(n)(s))  (Expression 35)

The inverse matrix operation unit 1402 calculates an inverse matrix ofthe channel ICI characteristic K′(s), and calculates the inversecharacteristic of the channel ICI characteristic 1411.

The channel ICI inverse characteristic multiplication unit 1403estimates carrier data by multiplexing a carrier signal 110 with theinverse characteristic 1412 of the channel ICI characteristic.

Note that it is carrier data that the inter-carrier interference removaldevice 1400 outputs. Therefore, similarly to the reception device shownin FIG. 17, the reception device that includes the inter-carrierinterference removal device 1400 does not have a channel estimation unitor an equalization unit but has a decode unit in later stage.

Thus, the inter-carrier interference removal device 1400 of Embodiment 3calculates a reliability value of a carrier based on the channelfrequency characteristic H estimated by the channel estimation unit 101,and weights the channel variation characteristic H′ with the reliabilityvalue. Consequently, the reliability value of the estimation of thechannel frequency characteristic including an ICI component (referred toas a channel ICI characteristic) can be enhanced.

Accordingly, carrier data can be obtained more accurately by removing anICI component. As a result, the reception performance at a high-speedmove in OFDM system is improved.

Embodiment 4

When there is interference in a received channel bandwidth, theinterference exerts a negative influence on the estimation of an ICIcomponent, and the effect of ICI removal is suppressed. The interferencemay be an NTSC (National Television System Committee) signal that is aterrestrial analog broadcasting signal, a CW (Continuous Wave)interference, etc. Especially in the NTSC signal, the interference maybe a video sub-carrier and a main audio sub-carrier narrowbandinterference.

According to Embodiment 4, such interference is detected, and a detectedresult is reflected to a reliability value of a carrier. Thus,degradation of the influence of the ICI removal can be prevented.

FIG. 19 is a block diagram showing the configuration of a reliabilityvalue calculation unit 2100 in an inter-carrier interference removaldevice in accordance with Embodiment 4.

As shown in FIG. 19, the reliability value calculation unit 2100 iscomposed of a channel judgment unit 2101, a judgment unit 2102 and aninterference judgment unit 2103.

The channel judgment unit 2101 performs the same function as thereliability value calculation unit 103 of Embodiment 1. That is to say,the channel frequency characteristic is inputted in a given function,and a reliability value is outputted as channel information.

The interference judgment unit 2103 detects interference of everycarrier.

FIG. 20 is a block diagram that shows the configuration of theinterference judgment unit 2103 in the inter-carrier interferenceremoval device of Embodiment 4.

The interference judgment unit 2103 is composed of an amplitude squareunit 2111, a symbol direction smoothing unit 2112, an intra-symbolsmoothing unit 2113, a multiplication unit 2114, and a comparison unit2115.

The amplitude square unit 2111 squares an amplitude of the channelvariation characteristic of each carrier and outputs the squareamplitude of the variation characteristic to the symbol directionsmoothing unit 2112.

The symbol direction smoothing unit 2112 smoothes the square amplitudeof the variation characteristic of each carrier in the symbol direction,and outputs the square amplitude to the intra-symbol smoothing unit 2113and the comparison unit 2115. In this embodiment, byway of example, thechannel variation characteristics of 128 symbols are smoothed, howeverthe number of the symbols is not limited to this.

The intra-symbol smoothing unit 2113 calculates an average of all thecarriers in the symbol that correspond to the smoothed square amplitudeof the variation characteristic outputted by the symbol directionsmoothing unit 2112, and outputs the average to the multiplication unit2114.

The multiplication unit 2114 multiplies a smoothed signal in the symbolwith a given coefficient, and outputs the result to the comparison unit2115. In this embodiment, the coefficient c is 16, for example, howeverthe coefficient c is not limited to this value.

The comparison unit 2115 compares, for every carrier, the output resultof the multiplication unit 2114 and the square amplitude of thevariation characteristic smoothed in the symbol direction. Thecomparison unit 2115 outputs the comparative result β_(n) of an n-thcarrier as interference information to the judgment unit 2102.

In this embodiment, the comparative result β_(n) has two values. Thesquare amplitude of the variation characteristic larger than the outputof the multiplication unit is represented by β_(n)=0, and the squareamplitude of the variation characteristic smaller than the output isrepresented by β_(n)=1. However, according to an amplitude of theinterference, multiple values are acceptable. The number of thecomparative result β_(n) is not limited to the above value.

The following describes an effect that is produced when the interferingjudgment unit 2103 is used.

When a carrier has narrowband interference, the reliability value of thepresent carrier is decreased and the channel characteristic of thecarrier has wide variations. The channel variation characteristic of thecarrier is relatively larger than an average of the channel variationcharacteristics of total carriers (output of the intra-symbol smoothingunit). Therefore, it can be judged that the carrier with a relativelylarge channel variation characteristic H′ compared with the average hasinterference.

In addition, smoothing the square in the symbol direction enables toenhance the detecting accuracy of interference.

The judgment unit 2102 outputs the reliability value based on thechannel information outputted by the channel judgment unit 2101 and theinterference information outputted by the interference judgment unit. Inthis embodiment, as shown in Expression 36, multiplication of thechannel information and the interference information is outputted as thereliability value W_(n).

Wn=f(H _(n))·β_(n)  (Expression 36)

The reliability value calculation unit 2100 configured as above is ableto specify a carrier in which interference occurs as well as to estimatethe reliability value of a carrier influenced by the channelcharacteristic. A reliability value is further determined with use ofthe specified carrier whose β=0 by the judgment unit 2102. An ICIcomponent is generated by weighting the carrier with use of thereliability value. Thus, it can be avoided to estimate an erroneous ICIcomponent from carriers with a low reliability value due to theinterference. Accordingly, the ICI component estimation accuracy isimproved, which brings about the improvement in the receptionperformance at a high-speed move.

Embodiment 5

In Embodiment 5, the inter-carrier interference removal device of thepresent invention is applied to a diversity reception device that uses aplurality of antennas.

First, differences between Embodiments 1 and 5 are described.

FIG. 21 is a block diagram of an inter-carrier interference removaldevice in accordance with Embodiment 5 of the present invention.

The channel frequency characteristic outputted by the channel estimationunit 101 and tentative carrier data outputted by the equalization unit102 are outputted to the outside of the inter-carrier interferenceremoval device. An output by the reliability value calculation unit 103is weighted by an output by the channel variation estimation unit 105.

An input to the ICI component estimation unit 106 is carrier data thatis obtained by branch combination that is described later.

FIG. 22 is a block diagram of a diversity reception device 2250 thatincludes an inter-carrier interference removal device 2201 of Embodiment5.

The inter-carrier interference removal device 2201 is equivalent to ICIremoval units 2663 and 2664 in the reception device.

The reception device 2250 includes a plurality of demodulation units2251 and 2252 installed at each branch and a combining unit 2253.

The demodulation unit 2251 is provided with an ICI removal unit 2263, achannel estimation unit 2265 and an equalization unit 2267. Similarly,the demodulation unit 2252 is provided with an ICI removal unit 2264, achannel estimation unit 2266 and an equalization unit 2268.

The combining unit 2253 is provided with carrier combining units 2281and 2284, a combined carrier weighting unit 2282 and a combined carrierreliability value calculation unit 2283.

In this embodiment, a demodulator that includes demodulation units fordiversity reception is called a branch or a system.

The reception device of Embodiment 5 is provided with two branches eachincluding the demodulation unit 2251 or the demodulation unit 2252.

The carrier combining units 2281 and 2284 each combines carrier data ofevery carrier outputted by the demodulation units (2251, 2252). In thisembodiment, Maximum Ratio Combining (MRC) is described as a combiningmethod. In the carrier combining unit 228, operation is processed asshown in the following expression.

Xc1^(˜) _(n)(s)={|H_(n)(s,1)|² ·X _(n)(s,1)+|H _(n)(s,2)|² }·X_(n)(s,2)}/(|H _(n)(s,1)|² +|H _(n)(s,2)|²)  (Expression 37)

Herein, Xc1^(˜)(s) is supposed to be

Xc1^(˜)(s)=[Xc1^(˜) ₀(s),Xc1^(˜) ₁(s), . . . ,Xc1^(˜)_(N−1)(s)]^(T)  (Expression 38)

X_(n)(s, b) and H_(n)(s, b) respectively show carrier data and channelfrequency characteristic of the n-th carrier in the s-th symbol's b-thsystem.

The combined carrier reliability value calculation unit 2283 calculatesa reliability value (combined carrier reliability value) of the combinedcarrier data 2315 for every carrier. The combined carrier weighting unit2282 weights the combined carrier data 2315 with the combined carrierreliability value.

Subsequently, the ICI removal units 2263 and 2264 of the demodulationunit are described in detail.

First, with use of the channel estimation results of H(s+1) and H(s−1),the variation component H′(s, b) is determined. In this embodiment, asshown in the following expression byway of example of calculation of thevariation component, the variation is determined with use of a symboladjacent to the (s−1)-th symbol and the (s+1)-th symbol.

H′ _(n)(s,b)={H _(n)(s+1,b)−H _(n)(s−1,b)}/(2·Ts)  (Expression 39)

Herein, H′(s, b) is supposed to be as follows.

H′(s,b)=diag(H′ _(n)(s,b))  (Expression 40)

In Embodiment 5, this H′ is weighted according to the reliability value.By way of example of this embodiment, weighting is processed based onH(s, b). In addition, the reliability value of the combined carrier data2315 is calculated and the combined carrier data 2315 is weighted. Basedon the weighted combined carrier data, an ICI component is estimated andremoved.

As the combined carrier reliability value calculated by the combinedcarrier reliability value calculation unit 2283, a total sum power ofall branches obtained by each carrier can be used. A reliability valuePc1_(n) of the n-th carrier is determined by the operation shown in thefollowing expression.

Pc1_(n)(s)=|H _(n)(s,1)|² +|H _(n)(s,2)|²  (Expression 41)

-   -   (n=0, N−1)

Herein, Pc1(s) is supposed to be as follows.

Pc1(s)=diag(Pc1_(n)(s))  (Expression 42)

Accordingly, the weighted combined carrier data is as follows.

Xc1̂(s)=Pc1(s)·Xc1^(˜)(s)  (Expression 43)

Xc1̂ (s) which is the combined carrier data Xc1^(˜) that is weighted isused as tentative carrier data to estimate an ICI component.Accordingly, an estimated value K_(n)(s, b) of an ICI component in then-th carrier of the s-th symbol's b-th system is as follows.

$\begin{matrix}\begin{matrix}{{K_{n}( {s,b} )} = {{\Xi \cdot \{ {{H^{\prime}( {s,b} )} \cdot {W( {s,b} )}} \} \cdot {Xc}}\; 1^{\hat{}}(s)}} \\{= {\Xi \cdot \{ {{{diag}( {H_{n}^{\prime}( {s,b} )} )} \cdot {{diag}( {w_{n}( {s,b} )} )}} \} \cdot}} \\{\{ {{{{diag}( {{Pc}\; 1_{n}(s)} )} \cdot {Xc}}\; 1^{\sim}(s)} \}}\end{matrix} & ( {{Expression}\mspace{14mu} 44} )\end{matrix}$

Thus, channel variation characteristic estimated for each branch isweighted with use of the channel characteristic w(s, b) of each branch.A tentative data symbol that is obtained by the diversity combining isweighted with use of the combined power Pc1(s). Thus, an ICI componentin the diversity configuration can effectively be removed.

Embodiment 6

In Embodiment 5, the combined carrier reliability value calculation unit2283 calculates the combined carrier reliability value based on thechannel frequency characteristic Hn. In Embodiment 6, a combined carrierreliability value is calculated based on the tentative carrier data andthe combined carrier data of each branch. Thus, a carrier that suffersfrom interferences is effectively judged, which suppresses erroneousestimation of an ICI component in the carrier.

Following is a description of when there are two branches.

FIG. 23 is a block diagram of an inter-carrier interference removaldevice 2301 that includes demodulation units 2251 and 2252 and acombining unit 2302.

A combined carrier reliability value calculation unit 2311 in thecombining unit 2302 calculates a combined carrier reliability valuebased on carrier data 2312 and 2313 and combined carrier data 2314 ofeach branch.

Following is a detailed description of the concrete calculation method.

Although an interference-free carrier whose channel has noises from atransmitter station to a reception device, a receiver can correctlyperform channel estimation. Accordingly, carrier data of each branch isconcentrated in the vicinity of a given signal.

On the other hand, in another carrier that is influenced byinterference, channel estimation is not correctly performed. Therefore,carrier data X_(n)(s, b) of each branch is dispersed from a given signalpoint.

Accordingly, when the distance between signal points of carrier data2312 and 2313 and signal points of combined carrier data 2314 for eachbranch is judged smaller than a given default threshold value, it can beaccurately judged if the carrier data is influenced by interference.

FIG. 24 schematically shows each distance between a signal point ofcarrier data of each branch and a signal point of combined carrier dataof each branch. In FIG. 24, the distance between the carrier dataX_(n)(s, b) and the combined carrier data Xc1(s) is represented by Ln(s,b), a threshold is represented by γ, and the number of branches isrepresented by b (bε1, 2).

First, for each branch, LEN_(n)(s, b) which is a difference between thethreshold γ and L_(n)(s, b) is evaluated.

LEN _(n)(s,1)=γ−L _(n)(s,1)  (Expression 45)

LEN _(n)(s,2)=γ−L _(n)(s,2)  (Expression 46)

In this embodiment, the threshold γ is a distance between symbols thatis determined by a modulation scheme. The polarity is judged by twovalues; if a value exceeds the threshold or not. In other words, eachpolarity of LEN_(n)(s, 1) and LEN_(n)(s, 2) is judged.

When the polarity is negative, the L_(n)(s, b) exceeds the threshold.Thus, the weight Pc1_(n)(s) is decreased. In this embodiment,Pc1_(n)(s)=0, for example.

Accordingly, a carrier that is influenced by interference is effectivelyjudged, and erroneous estimation of an ICI component of the carrier canbe suppressed.

Note that when there are four branches, LEN, can be expressed asfollows.

LEN _(n)(s,1)=γ−L _(n)(s,1)  (Expression 47)

LEN _(n)(s,2)=γ−L _(n)(s,2)  (Expression 48)

LEN _(n)(s,3)=γ−L _(n)(s,3)  (Expression 49)

LEN _(n)(s,4)=γ−L _(n)(s,4)  (Expression 50)

Among the four expression (See FIG. 25), when three of the expressionsare negative, in other words, the three exceeds the threshold,Pc1_(n)(s)=0 is established.

In this embodiment, the number of LEN, whose polarity is negative isthree. However, this number may be any given number. The larger thenumber is, the harder it is to detect interference.

Also, multiple values may be used for the judgment with use of the sumof the distances (LEN_(n)(s, 1)+LEN_(n)(s, 2)).

In addition, a combined carrier reliability value may be calculatedbased on results of a hard decision performed on the tentative carrierdata and the combination carrier data of each branch with use of thesignal points.

Suppose the hard decision results of the tentative carrier data and thecombined carrier data for each branch are respectively X_(n)(s, 1)″,Xc1(s)″,

X _(n)(s,1)″=Xc1(s)″  (Expression 51)

X _(n)(s,2)″=Xc1(s)″  (Expression 52)

out of the above two evaluation expressions, the reliability value isjudged based on the number of established expressions.

In this embodiment, when the hard decision result for each branch andthe hard decision result of combined carrier data match in all branches,the reliability value is deemed to be high, and Pc1_(n)(s)=1. When nobranches match each other, the reliability value is deemed to be low,and Pc1_(n)(s)=0.

Note that when there are four branches,

X _(n)(s,1)″=Xc1(s)″  (Expression 53)

X _(n)(s,2)″=Xc1(s)″  (Expression 54)

X _(n)(s,3)″=Xc1(s)″  (Expression 55)

X _(n)(s,4)″=Xc1(s)″  (Expression 56)

out of the four evaluation expressions, the reliability value is judgedaccording to the number of established expressions,

Thus, the interference can be detected based on a signal point of thetentative carrier data of each branch and a signal point of the combinedcarrier data of each branch. As a result, erroneous estimation of an ICIcomponent in the carrier is suppressed.

In the above description, the distance L, between the carrier dataX_(n)(s, b) and the combined carrier data Xc1(s) is what is called theEuclidean distance. However, as shown in the following expression,distances in an in-phase component (real number unit) and an orthogonalcomponent (imaginary number unit) are respectively obtained, and the sumL_(n) of these distances is obtained. Thus, the evaluation can besimilarly performed. Since this operation is simpler than thecalculation of the Euclidean distance, a hardware circuit can beomitted. The Re[x] represents an in-phase component (real number unit)of a complex number x, and the Im[x] represents an orthogonal component(imaginary number unit) of the complex number x.

L_(n)(s) = abs[Re[X_(n)(s, b)] − Re[Xc 1(s)]] + abs[Im[X_(n)(s, b)] − Im[Xc 1(s)]]

In addition, the evaluation can be made with use of the distanceL_(n)(s) that is smoothed for a given period (referred to as a smootheddistance: Fil [L_(n)]). As the smoothed distance, an average determinedby using information ranging from hundreds or thousands symbols in asymbol direction and from several or tens of carriers in a carrierdirection, or a smoothed value with use of an IIR filter.

In concrete, in Expressions 45-50, the smoothed distance: Fil[L_(n)] isused instead of the distance L_(n)(s) to evaluate a difference betweenthe smoothed distance and the threshold is evaluated. Thus, wheninterference is contained in specific carriers for more than severalsymbols continuously, even if the threshold γ and the distance L_(n)(s)accidentally approximate each other in a certain symbol, interferencepresence can be effectively judged.

In addition, a value based on the smoothed distance Fil [L_(n)] may beused as the threshold y to evaluate a difference between the smootheddistance and the distance L_(n)(s) in a certain symbol. The threshold γis not limited to the average of the distance L_(n) but may be anintegral multiplication or a singular multiplication of the average.Thus, the threshold according to the degree of interference presence canbe set. Accordingly, when interference is contained in specific carriersfor several symbols continuously, the interference presence can beeffectively judged.

As for the smoothing of the smoothed distance Fil[L_(n)], note thatalthough the smoothing in both the symbol and carrier directionsproduces a greater effect, the smoothing may be performed in either oneof the directions.

Embodiment 7

In Embodiment 7, the combined carrier reliability value calculation unitcalculates the combined carrier reliability value based exclusively onthe tentative carrier data of each branch.

FIG. 26 is a block diagram showing the configuration of an inter-carrierinterference removal device 2401 that includes the demodulation units2251 and 2252 and the combining unit 2402 installed in a receptiondevice in accordance with Embodiment 7.

A combined carrier reliability value calculation unit 2411 in thecombining unit 2402 calculates a combined carrier reliability valuebased exclusively on tentative carrier data 2412 and 2413 of eachbranch.

For example, when there are more than two branches, the description ofthe paragraph 0041 of Patent Document (Laid-Open 2006-41980) and a casebased on a hard decision result may be applied. When there are more thanfour branches, the description of the paragraphs 0079 and 0088 of PatentDocument (Laid-Open 2006-41980) may be applied.

Embodiment 8

Equalized tentative carrier data used for ICI removal have errors due topresence of noises or interference. However, the carrier data,originally, has a given signal point arrangement by being demodulated bytransmission data.

In Embodiment 8, when the amplitude is extremely large, ICI with givenamplitudes is removed by the clip processing.

FIG. 27 is a block diagram of an inter-carrier interference removaldevice that includes a block that performs a clip processing ontentative carrier data.

A clip processing unit 2401 performs the clip processing

on weighted carrier data, and outputs the weighted carrier data to theICI component estimation unit 106.

Shown as below, The clip processing unit 2401 performs the clipprocessing on carrier data with given amplitudes. An example is shownwhere the clip processing is performed on in-phase components andorthogonal components of carrier data with amplitudes of pilot carriers.

FIG. 28 is a view schematically showing amplitudes the clip processingunit 2401 performs the clip processing. Black circles each indicate apossible position of a signal point when 64-QAM is used. The amplitudesof the in-phase component and the orthogonal component ranges between ±1at the maximum. White circles each indicate a position of a pilotcarrier.

Pilot carriers are positioned at ±4/3 on the in-phase component.

Basically, tentative carrier data is demodulated and positioned at givensignal points (positions at the black circles in FIG. 28). However, dueto the presence of noises and interference, the tentative carrier datamay be positioned far from the given signal points and have largeramplitude.

When the carrier data A and B shown in FIG. 28 each exceed ¾ of thein-phase axis and −¾ of the orthogonal axis, each of the carrier data Aand B is clipped at ¾ of the in-phase axis and −¾ of the orthogonalaxis.

In Embodiment 8, a clip level of carrier data is determined by anamplitude level of a pilot carrier. However, Embodiment 8 is not limitedto this.

Embodiment 9

A reception device in accordance with Embodiment 9 of the presentinvention is described with reference to FIGS. 29-35.

FIG. 29 is a block diagram showing the diversity reception device inaccordance with Embodiment 9.

The reception device includes: antennas 3001 and 3101; RF units 3002 and3102 that each select a reception signal of a desired reception channel;reception processing units 3021 and 3121 each of which performsdemodulating processing; a first combining unit 3011; a second combiningunit 3012; an error correction unit 3003 that performs error correctionon a signal outputted from the second combining unit 3012; a decode unit3004 that decodes a signal that is compressed by MPEG-2 (Moving PictureExperts Group) and the like and is performed error correction by theerror correction unit 3003; and a display unit 3005 that outputs imagesand sounds decoded by the decode unit 3004.

FIG. 30 is a block diagram showing the configuration of the receptionprocessing unit 3021.

Note that the configuration of the reception processing unit 3121 isbasically identical with that of the reception processing unit 3021.Only a difference between the reception processing units 3021 and 3121is that the reception processing unit 3121 receives an input signaloutputted from the RF unit 3102. Therefore, only the configuration ofthe reception processing unit 3021 is described.

The reception processing unit 3021 is composed of an A/D unit 3031, aquadrature demodulation unit 3032, an FFT unit 3033, a symbolsynchronization unit 3034, and a demodulation unit 3041.

The A/D unit 3031 converts an output from the RF unit 3002 from ananalogue to digital signal. The quadrature demodulation unit 3032performs quadrature demodulation on the digital signal converted by theA/D unit 3031, and thus converts the digital signal to a complexbaseband signal. The quadrature demodulation unit 3032 outputs thecomplex baseband signal to the FFT unit 3033 and the symbolsynchronization unit 3034.

The symbol synchronization unit 3034 synchronizes in an OFDM symbolinterval, and outputs a symbol position information signal to the FFTunit 3033.

Based on the symbol position information signal, the FFT unit 3033performs the Fourier transform on the quadrature demodulated signal, andconverts the signal into a signal in a frequency domain, and outputs thesignal to the demodulation unit 3041.

FIG. 31 is a block diagram showing the configuration of the demodulationunit 3041.

The demodulation unit 3041 is composed of a first reception signaldemodulation unit 3095 and a second reception signal demodulation unit3096.

The first reception signal demodulation unit 3095 is composed of a firstchannel estimation unit 3051 and a first equalization unit 3052. Thesecond reception signal demodulation unit 3096 is composed of an ICIcomponent generation unit 3053, a subtraction unit 3054, a secondchannel estimation unit 3056 and a second equalization unit 3055.

As shown in FIG. 32, the first channel estimation unit 3051 is composedof: an SP generation unit 3061 that generates a known signal that is SP(Scattered Pilot); an SP extraction unit 3062 that extracts the SPsignal from an input signal; a division unit 3063; and an interpolationunit 3064.

Note that the second channel estimation unit 3056 has basicallyidentical units with the first channel estimation unit 3051. In thisembodiment, the SP signal is a reference signal, which is inserted intoa transmission signal in a transmission system of terrestrial digitaltelevision broadcasting. The SP signal is basically identical with thepilot symbol described in the above embodiments.

The SP extraction unit 3062 extracts the SP signal from the post-FFTsignal. The division unit 3063 divides the SP signal by the known signalgenerated by the SP generation unit 3061. Thus, a channel characteristicof the SP signal is calculated.

Based on the calculated channel characteristic of the SP signal, theinterpolation unit 3064 performs interpolation processing, andcalculates channel characteristics of other signals than the SP signal.

In the first equalization unit 3052, a transmission signal is estimatedby dividing the post-FFT signal by the calculated channelcharacteristic. A tentatively-equalized signal is outputted to the firstcombining unit 3011 shown in FIG. 29.

The channel characteristic calculated by the first channel estimationunit 3051 is also outputted to the first combining unit 3011.

The first combining unit 3011 performs diversity combining on eachtentatively-equalized signal with use of the channel characteristicsoutputted by the reception processing units 3021 and 3121.

When the tentatively-equalized signal and the channel characteristic atthe reception processing unit 3021 are expressed as X1_(n) ^(˜)(s, 1)and H1_(n)(s, 1) respectively, and the tentatively-equalized signal andthe channel characteristic at the reception processing unit 3121 areexpressed as X1_(n) ^(˜)(s, 2) and H1_(n)(s, 2) respectively, thetentatively-equalized signals are combined with use of maximum ratiocombining as shown in Expression 57.

Xc1_(n)(s)=(|H1_(n)(s,1)|² ·X1_(n)(s,1)+|H1_(n)(s,2)|² ·X1_(n)^(˜)(s,2))/(|H1_(n)(s,1)|² +|H1_(n)(s,2)|²)  (Expression 57)

The combining method is not limited to Expression 57, and aheretofore-known diversity combining method can be applied.

The signals combined by the first combining unit 3011 are outputted tothe reception processing units 3021 and 3121.

Note that the output from the first combining unit 3011 may be outputtedto the reception processing units 3021 and 3121 after the hard decisionaccording to a transmission code point.

The output signal of the first combining unit 3011 is inputted into theICI component generation unit 3053. The channel characteristic estimatedby the first channel estimation unit 3051 is also inputted into the ICIcomponent generation unit 3053. Various methods are suggested forestimating an ICI component. This embodiment employs the ICI componentestimation method described in Nonpatent Document 3.

As shown in FIG. 33, the ICI component generation unit 3053 is composedof a channel characteristic linear differential calculation unit 3091and a multiplication unit 3092.

The channel characteristic linear differential calculation unit 3091inputs a channel characteristic. With use of Expression 57, thecharacteristic linear differential calculation unit 3091 calculates alinear differential of channel characteristics of symbols in thevicinity of the present symbol (symbol number: p), and outputs thelinear differential to the multiplication unit 3092.

The multiplication unit 3092 multiplies together the combined signal X˜that is an output from the first combining unit 3011, and an outputsignal from the channel characteristic linear differential calculationunit 3091, and the constant matrix Ξ shown in Expressions 3 and 4. Thisoperation is as shown in Expression 2. Thus, the ICI component isestimated and generated.

The method disclosed in Nonpatent Document 3 is employed as the ICIcomponent generation method in the ICI component generation unit 3053.However, the generation method is not limited to this, andheretofore-known methods may be employed.

The subtraction unit 3054 subtracts the estimated ICI component from thepost-FFT signal. As a result, the ICI component is removed.

Due to the diversity effect, the output signal of the first combiningunit 3011 is a more reliable transmission signal than that of the firstequalization unit 3052. As a result, accuracy of the ICI componentgeneration is improved, and ICI can be removed more accurately.

Based on the output signal of the subtraction unit 3054, a channelcharacteristic of the signal after the ICI component removal isestimated by the second channel estimation unit 3056.

Thus, the channel characteristic of a signal from which ICI has beenremoved is calculated.

In the second equalization unit 3055, a transmission signal is estimatedagain by subtraction with use of the channel characteristic estimatedfrom the output signal of the subtraction unit 3054.

Since an equalized signal outputted from the second equalization unit3055 is less affected by ICI, estimation accuracy of the equalizedsignal is more improved than the output signal of the first equalizationunit 3052.

The output signal of the second equalization unit 3055 and the channelcharacteristic estimated by the second channel characteristic estimationunit 3056 are outputted to the second combining unit 3012.

The second combining unit 3012 performs diversity combining on eachsignal that has been secondarily equalized, with use of the channelcharacteristics of the ICI-removed signals each outputted from thereception processing units 3021 and 3121.

When the secondarily-equalized signal and the channel characteristic ofthe ICI-removed signal at the reception processing unit 3021 areexpressed as X2_(n) ^(˜)(s, 1) and H2_(n)(s, 1) respectively, and thesecondarily-equalized signal and the channel characteristic of theICI-removed signal at the reception processing unit 3121 are expressedas X2_(n) ^(˜)(s, 2) and H2_(n)(s, 2) respectively, thesecondarily-equalized signals are combined with use of maximum ratiocombining as shown in Expression 58 for diversity combining.

Xc2_(n)(s)=(|H2_(n)(s,1)|² ·X2_(n)(s,1)+|H2_(n)(s,2)|²·X2_(n)(s,2))/(|H2_(n)(s,1)|² +|H2_(n)(s,2)|²)  (Expression 58)

The combining method is not limited to Expression 58, and aheretofore-known diversity combining method can be used.

In this embodiment, the first combining unit 3011 and the secondcombining unit 3012 are described with use of the same maximum ratiocombining. However, the first combining unit 3011 combines signalsinfluenced by ICI, and the second combining unit 3012 combinesICI-removed signals. Considering both combining units combines thesignals with different characteristics, note that a different diversitycombining method may be performed by the first combining unit 3011 fromby the second combining unit 3012.

Furthermore, the first channel estimation unit 3051 and the secondchannel estimation unit 3052 are described as if these were identical toeach other. However, the first channel estimation unit 3051 estimatesthe channel characteristic of the signal influenced by ICI, and thesecond channel estimation unit 3056 estimates the channel characteristicof the ICI-removed signal. Considering both estimation units estimatesthe signals with the different characteristics, note that a differentestimation method can be used between the first channel estimation unit3051 and the second channel estimation unit 3056.

Note that without the second channel estimation unit 3056, and that thesecondary equalization and the secondary diversity combining may beperformed with use of the channel characteristic estimated by the firstchannel estimation unit 3051. However, since the ICI removal changes thechannel characteristic of the signal from which ICI has not been removedyet, the equalization and the diversity combining after the ICI removalare more effective.

The second combining unit 3012 performs diversity combining on theICI-removed signals. The combined signals are outputted to the errorcorrection unit 3003, and afterwards are decoded and displayed.

Due to the diversity effect, the output signal of the second combiningunit 3012 is a more reliable transmission signal than eachsecondarily-equalized signal of the reception processing units 3021 and3121. Accordingly, the reception performance improves.

With the above configuration, by performing the diversity combining ontentatively-equalized signals so as to generate an ICI component, thereliability value of the tentatively-equalized signals is enhanced, andthe ICI component is estimated, in each demodulation unit, with use ofthe reliability value. Thus, estimation accuracy of the ICI component ineach demodulation unit is improved, and as a result, ICI removal iseffectively performed.

In addition, a channel characteristic is calculated again after the ICIremoval. Optimum equalization and diversity combining with use of thechannel characteristic enhance the estimation accuracy of a finaltransmission signal. Accordingly, the reception device is more robustagainst ICI or noises, and is able to exhibit stable and high-qualityreception performance during moving or in a weak electrical fieldenvironment.

Furthermore, in this embodiment, the diversity combining has two steps.However, the number of the steps is not limited to this, and there maybe more than three steps so as to remove ICI step-by-step.

For example, FIGS. 34, 35 and 36 each show a configuration diagram of adiversity reception device whose diversity combining is processed inthree steps.

A demodulation unit 3042 in FIG. 36 estimates the channel characteristicof the ICI-removed signal every time the ICI removal is performed, andperforms equalization and diversity combining with use of the channelcharacteristic.

By performing the step-by-step ICI removal, estimation accuracy of thetransmission signal is further improved, and high-quality and stablereception performance can be achieved even during moving or in a weakelectrical field environment.

To realize the reception device of Embodiment 9, a program that performsat least part of the reception processing may be used. Also, a receptionmethod that performs part of the reception processing in the receptiondevice may be used.

Furthermore, any combination of the reception device, the receptionmethod, a reception circuit or the program that performs part of thereception processing to realize the reception device of Embodiment 9 maybe used.

Embodiment 10

A reception device in accordance with Embodiment 10 of the presentinvention is described with reference to FIGS. 37, 38, and 39. Theidentical units with the aforementioned units have the identicalnumerals and a description of the identical units is omitted.

FIG. 37 is a block diagram of a diversity reception device in accordancewith Embodiment 10 of the present invention.

The diversity reception device of Embodiment 10 performs feedback on adiversity combining signal, which is a different configuration from thediversity reception device of Embodiment 9.

FIG. 39 is a block diagram of a demodulation unit 3045.

The demodulation unit 3045 is composed of an ICI component generationunit 3083, a subtraction unit 3054, an equalization unit 3081, and achannel estimation unit 3082.

An output signal from an FFT unit 3033 is inputted into the subtractionunit 3054. The subtraction unit 3054 subtracts output from the ICIcomponent generation unit 3083.

In the first iteration, the output from the ICI component generationunit 3083 is zero.

The output signal from the subtraction unit 3054 is inputted into theequalization unit 3081 and the channel estimation unit 3082. The channelestimation unit 3082 estimates a channel characteristic, and outputs anestimation result to the equalization unit 3081 and the combining unit3015.

The channel estimation unit 3082 is equivalent to the first channelestimation unit 3051 of Embodiment 9.

The equalization unit 3081 estimates a transmission signal by dividingthe ICI-removed signal by the estimated channel characteristic, andoutputs an equalized signal to the combining unit 3015.

A reception processing unit 3125 has a basically identical configurationwith a reception processing unit 3025. Since only a difference betweenthe demodulation units 3125 and 3025 is that the input signal is not theoutput signal from the RF unit 3002 but from the RF unit 3102, adescription of the reception processing unit 3125 is omitted.

In FIG. 37, the reception processing units 3025 and 3125 outputs channelcharacteristics and equalized signals, and the combining unit 3015performs diversity combining on the equalized signals according to thechannel characteristics.

Similarly to Embodiment 9, Expression 57 may be used for the diversitycombining. However, the diversity combining is not limited to Expression1, and a heretofore-known expression may be used.

This combined signal is inputted into the ICI component generation unit3083 in each of the reception processing units 3025 and 3125.

Note that when the combined signal is inputted into the ICI componentgeneration unit 3083, the combined signal may be performed a harddecision according to a code point.

Thus, the ICI component generation unit 3083 estimates and generates anICI component, based on the channel characteristic and the output fromthe combining unit 3015, and the ICI component is subtracted from thepost-FFT signal by the subtraction unit.

A difference of the ICI component generation unit 3083 from the ICIcomponent generation unit 3053 of FIG. 33 is that the channelcharacteristic linear differential unit 3091 performs a calculation withuse not of Expression 1 but of Expression 59. However, the expression isnot limited to this.

H′(s)=(H(s)−H(s−1))/Ts  (Expression 59)

Repeating this iteration within a symbol interval improves estimationaccuracy of an equalized signal.

In the last iteration within the symbol interval, the combined signal isoutputted to the error correction unit 3003, and accordingly, errorcorrection is performed on the combined signal.

In the subsequent symbol interval, a new iteration starts for a post-FFTsignal corresponding to the symbol. When the first iteration starts, asignal in the ICI component generation unit 308 is reset to zero.

A signal from which ICI has been removed and on which diversitycombining has been performed in each reception processing unit isrecursively used for ICI component generation, which improves accuracyof ICI component estimation in each reception processing unit. The moreiterations are repeated, the less influence from noises or ICI isresulted. Thus, with this configuration, ICI removal is effectivelyperformed.

In addition, when iterations are further repeated, a circuit size can bereduced compared with Embodiment 9. As a result, the reception device ismore robust against ICI or noises, and is able to exhibit stable andhigh-quality reception performance during moving or in a weak electricalfield environment.

In the embodiment, the description is made with use of the diversityconfiguration having two antennas. Note that the diversity configurationmay have more than two antennas. The reception performance can befurther improved by increasing the number of the antennas and thedemodulation units.

Furthermore, each constituent of the reception device of Embodiment 10may be implemented in an integrated circuit. In such a case, eachconstituent may be individually integrated on one chip, or part or allof the constituents may be integrated on one chip.

Furthermore, a program that performs at least part of the receptionprocessing of the reception device in accordance with the embodiment maybe used. In addition, a reception method that performs at least part ofthe reception processing of the reception device of Embodiment 10 may beused.

Also, any combination of the reception device, the reception method, thereception circuit, and the program that performs part of the receptionprocessing to realize the reception device of Embodiment 10 may be used.

Furthermore, in Embodiments 9 and 10, the description is made that theA/D unit 3031 is immediately before the quadrature demodulation unit3032. However, the A/D unit 3031 may be contained in a tuner,immediately after the quadrature demodulation unit 3032, or at otherposition.

Also, in Embodiments 9 and 10, the diversity configuration using twoantennas is described. However, the diversity configuration may use morethan two antennas. Increasing the number of antennas and demodulationunits further improves the reception performance.

Furthermore, the diversity configuration is not limited to the space orangle diversity having more than two antennas.

A frequency diversity or a time diversity may be performed with use ofone antenna.

Also, the demodulation unit does not need to be plural. The function ofthe demodulation unit may be realized by using memory ormultiprocessing.

Also, in Embodiments 9 and 10, the description is made that the signalsis an OFDM signal used in the terrestrial digital broadcasting wave.However, signals may be in any forms as long as multi-carriertransmission is used. In addition, the description is made on theconfiguration to remove ICI. However, as long as an interferencecomponent contained in a reception signal is generated and removed froman estimated transmission signal, the present invention may be appliedto any interference removal techniques. In such a case, instead of theICI component generation unit 3053, an interference component generationunit that estimates and generates an interference component to beremoved may be used.

<Supplementation>

The present invention is described according to the above embodiments.Note that the present invention is never limited to the embodiments, andthe present invention includes the following cases.

(1) In the carrier combination (maximum ratio combining) shown in theabove embodiments, with use of the channel frequency characteristics,H_(n)(s, 1) and H_(n)(s, 2), and the output signals from theequalization unit, X_(n)(s, 1) and X_(n)(s, 2) that are obtained in eachdemodulation unit, the combination is performed as follows:

Xc _(n)(s)=(|H _(n)(s,1)|² ·X _(n)(s,1)+|H _(n)(s,2)|² ·X _(n)(s,2))/(|H_(n)(s,1)|² +|H _(n)(s,2)|²)  (Expression 60)

However, each equalization unit can be omitted, and the followingcombination can be applied with use of the carrier signals Y_(n)(s, 1)and Y_(n)(s, 2) and the channel frequency characteristics, H_(n)(s, 1)and H_(n)(s, 2).

Xc _(n)(s)=(H _(n)(s,1)*·Y _(n)(s,1)+H _(n)(s,2)*·Y _(n)(s,2))/(|H_(n)(s,1)|² +|H _(n)(s,2)|²)  (Expression 61)

Note that “*” represents complex conjugate.

This applies to a diversity reception device that includes a pluralityof carrier combining units and that performs multiple times of carriercombining. For example, as shown in FIG. 22, suppose the carriercombining unit 2281 is the first carrier combining unit, and that thecarrier combining unit 2284 is the second carrier combining unit, in them-th carrier combining unit, the carrier signal is expressed asYm_(n)(s, b), the channel frequency characteristic as Hm_(n)(s, b), andthe combined carrier data as Xcm_(n)(s, b). Consequently, Expression 61can be expressed as the following escape sequence.

Xcm _(n)(s)=(Hm _(n)(s,1)*·Ym _(n)(s,1)+Hm _(n)(s,2)*·Ym _(n)(s,2))/(|Hm_(n)(s,1)|² +|Hm _(n)(s,2)|²)  (Expression 62)

The above carrier combination method is applied in the carriercombination of the aforementioned embodiments as follows.

As for Embodiment 5, the equalization unit 102 and the equalization unit(unillustrated) that includes the ICI removal unit 2264 in FIGS. 21 and22 may be omitted. A combined signal may be calculated, with use ofExpression 62, in the carrier combining unit 2281 based on the outputfrom the FFT units 2261 and 2262, and the channel characteristicsobtained in the ICI removal units 2263 and 2264.

Furthermore, the equalization units 2267 and 2268 may be omitted. Thecarrier combining unit 2281 may calculate a combined signal, with use ofExpression 62, based on the output from the ICI removal operation unit107 and outputs from the ICI removal operation unit (unillustrated)included in the ICI removal unit 2264 and the channel estimation units2265 and 2266.

Furthermore, the above applies to FIG. 23 of Embodiment 6 and FIG. 26 ofEmbodiment 7. In addition, in Embodiment 9 shown in FIGS. 29, 30 and 31,the first equalization unit 3052 and the first equalization unit(unillustrated) included in the reception processing unit 3121 may beomitted. The first carrier combining unit 3011 may calculate a combinedsignal with use of Expression 62 based on the output from the FFT unit3033 and the FFT unit (unillustrated) included in the receptionprocessing unit 3121 and outputs from the first channel estimation unit3051 and the first channel estimation unit (unillustrated) included inthe reception processing unit 312 (unillustrated).

Furthermore, the second equalization unit 3055 and the secondequalization unit (unillustrated) included in the reception processingunit 3121 may be omitted. The second carrier combining unit 3012 maycalculate a combined signal, with use of Expression 62, based on theoutput from the subtraction unit 3054 and the subtraction unit(unillustrated) included in the reception processing unit 3121 andoutputs from the second channel estimation unit 3056 and the secondchannel estimation unit (unillustrated) included in the receptionprocessing unit 3121.

In addition, the above applies to Embodiment 9 in which there are morethan two combining units, as shown in FIGS. 34, 35 and 36. The thirdequalization unit 3074 and a third equalization unit (unillustrated)included in the reception processing unit 3122 may be omitted. The thirdcarrier combining unit 3013 may calculate a combined signal, with use ofExpression 62, based on the output from the subtraction unit 3073 and asubtraction unit (unillustrated) included in the reception processingunit 3122 and outputs from the third channel estimation unit 3075 and asecond channel estimation unit (unillustrated) included in and thereception processing unit 3122.

Furthermore, as for Embodiment 10 shown in FIGS. 37, 38 and 39, theequalization unit 3081 and the equalization unit (unillustrated)included in the reception processing unit 3125 may be omitted. Thecombining unit 3015 may calculate a combined signal with use ofExpression 62 based on the output from the subtraction unit 3054 and thesubtraction unit (unillustrated) included in the reception processingunit 3125 and outputs from the channel estimation unit 3082 and thechannel estimation unit (unillustrated) included in the receptionprocessing unit 3125.

(2) The above embodiments show the OFDM signal whose conversion betweenthe time domain and the frequency domain is based on FFT, and itsrelating demodulation processing. However, the present invention isapplicable to multi-carrier signals that are a plurality of carriersmultiplexed on the frequency axis. For example, the multi-carriersignals may be performed wavelet transform, cosine transform, orHadamard transform.

(3) Part or all of the constituents of the above reception device andthe inter-carrier interference removal device may be composed of onesystem LSI (Large Scale Integration). The system LSI ishyper-multifunctional LSI that integrates a plurality of components onone chip. The plurality of components may be individually on one chip,or part or all of the components may be integrally on one chip. AlthoughLSI is referred here, according to degrees of integration, LSI can bereferred to as IC, system. LSI, super LSI, or ultra LSI.

In addition, the LSI is not the only method for making an integratedcircuit. An integrated circuit may be realized by a dedicated circuit ora general processor. FPGA (Field Programmable Gate Array) that isprogrammable after the LSI is produced, or a reconfigurable processorthat is reconfigurable of connection and setting of a circuit cellinside LSI may be used.

Furthermore, if the advance of the technology or a derivative of anothertechnology creates a new technology of the integrated circuit that canreplace the LSI, as a matter of course, functional blocks can beintegrated with use of the new technology. Biotechnology and such mayhave the potential to be applied for the new technology.

(4) The reception device and the inter-carrier interference removaldevice may be a computer system composed of, specifically, a microprocessor, ROM, RAM, a hard disk unit, a display unit, a keyboard, amouse and the like. The RAM and the hard disk unit record a computerprogram. In response to the operation by the micro processor accordingto the computer program, each device can achieve its function. Thecomputer program is constituted from a plurality of instruction codesthat indicate instructions to a computer.

(5) Part or all of the constituents of the above reception device andthe inter-carrier interference removal device may be composed of aremovable IC card or a stand-alone module. The IC card and the moduleare each computer system composed of a micro processor, ROM, RAM, andthe like. Each of the IC card and the module may include thehyper-multifunctional LSI. In response to the operation by themicroprocessor according to the computer program, each of the IC cardand the module can achieves its function. The IC card and the module maybe tamper-resistant.

(6) The present invention may be the methods shown as above.Alternatively, the present invention may be a computer program thatrealizes these methods with a computer, or digital signals composed ofthe computer program.

Furthermore, the present invention may be the computer program or thedigital signals that are recorded on a computer readable recordingmedium such as a flexible disk, a hard disk, CD-ROM, MO, DVD, DVD-ROM,DVD-RAM, BD (Blu-Ray Disc), and semiconductor memory. The presentinvention may also be the computer program or the digital signalsrecorded on the above computer readable recording medium.

(7) Some of the embodiments and the modifications may be combined to oneanother.

INDUSTRIAL APPLICABILITY

Since the inter-carrier interference removal device and the receptiondevice using the same in accordance with the embodiments of the presentinvention are able to remove inter-carrier interference caused byDoppler shift contained in a carrier signal, the inter-carrierinterference removal device can improve the reception characteristic inreceiving the multi-carrier signal in a mobile condition. Accordingly,the present invention is useful as the reception device that receives,in the cars or trains moving at a high speed, digital terrestrialbroadcasting and wireless LAN signals in OFDM.

1-29. (canceled)
 30. A reception device that performs diversityreception, comprising: a plurality of reception processing units eachoperable to receive a reception signal via an antenna that correspondsto one of the reception processing units, and demodulate the receptionsignal; a first combining unit operable to (i) receive first outputsignals from the reception processing units, (ii) perform diversitycombining on all the first output signals, (iii) perform hard decisionon the combined signal according to a transmission code position, and(iv) output a hard decision result to each reception processing unit;and a second combining unit operable to (i) receive second outputsignals from the reception processing units, and (ii) perform diversitycombining on the second output signals, wherein each receptionprocessing unit includes: a first reception signal processing unit thatgenerates one of the first output signals by demodulating the receptionsignal, and outputs the one of the first output signals to the firstcombining unit; and a second reception signal processing unit that (i)generates one of the second output signals by demodulating the receptionsignal with use of the combined signal received from the first combiningunit, and (ii) outputs the one of the second output signals to thesecond combining unit.
 31. A reception device that performs diversityreception, comprising: a plurality of reception processing units eachoperable to receive a reception signal via an antenna that correspondsto one of the reception processing units, and demodulate the receptionsignal, and a combining unit operable to (i) receive output signals fromthe reception processing units, (ii) perform diversity combining on allthe output signals, and (iii) output a combined signal to each receptionprocessing unit, wherein each reception processing unit receives thecombined signal from the combining unit, and demodulates the receptionsignal with use of the combined signal.
 32. The reception device ofclaim 31, further comprising: a combined carrier reliability calculationunit operable to calculate a reliability value of a combined carrierthat results from the diversity combining by the reception deviceperforming the diversity reception; a combined carrier weighting unitoperable to weight the combined carrier with use of the reliabilityvalue; and a combined carrier output unit operable to output, to thereception processing unit, tentatively combined carrier having beenweighted with use of the reliability value, so that the tentativelycombined carrier is to be processed by the reception processing unit.33. The reception device of claim 32, wherein the combined carrierreliability calculation unit calculates the reliability value based on asum of carrier power of each branch.
 34. The reception device of claim32, wherein the combined carrier reliability calculation unit calculatesthe reliability value based on a difference between (i) a giventhreshold and (ii) a distance between reception signal points of carriersignals of different branches.
 35. The reception device of claim 32,wherein the combined carrier reliability calculation unit calculates thereliability value based on a difference between (i) a given thresholdand (ii) a distance from a reception signal point of a carrier signal ofeach branch to a signal point of a combined signal.
 36. The receptiondevice of claim 31, wherein each reception processing unit includes: anorthogonal transform unit that performs orthogonal transform on thereception signal; and an interference component removal equalizationunit that removes an interference component from theorthogonally-transformed reception signal, and equalizes the receptionsignal, the interference component removal equalization unit including:an interference component generation unit that generates an interferencecomponent in the reception signal with use of a channel characteristicand a combined signal received at the combining unit; a subtraction unitthat performs a subtraction so as to remove the interference componentfrom the reception signal; a channel estimation unit that estimates achannel characteristic of an output signal of the subtraction unit; andan equalization unit that generates an equalized signal by dividing theoutput signal by the channel characteristic, and the combining unitgenerates, according to the channel characteristic estimated by thechannel estimation unit in each reception processing unit, the combinedsignal by performing diversity combining on the equalized signal at eachreception processing unit, and outputs the combined signal.
 37. Areception device that performs diversity reception, the reception deviceincluding a plurality of reception processing units, a first combiningunit, and a second combining unit, wherein each reception processingunit includes: an orthogonal transform unit that performs orthogonaltransform on the reception signal; and an interference component removalequalization unit that removes an interference component from theorthogonally-transformed reception signal, and equalizes the receptionsignal, the interference component removal equalization unit including:a first channel estimation unit that estimates a channel characteristicof the orthogonally-transformed reception signal; a first equalizationunit that equalizes the orthogonally-transformed reception signal byperforming a division by the channel characteristic; an interferencecomponent generation unit that receives a combined signal from the firstcombining unit, and generates an interference component in theorthogonally-transformed reception signal with use of the combinedsignal and the channel characteristic; a subtraction unit performs asubtraction so as to remove the interference component from theorthogonally-transformed reception signal; a second channel estimationunit that estimates a channel characteristic of an output signal of thesubtraction unit; and a second equalization unit that equalizes theoutput signal by a division by the channel characteristic, the firstcombining unit generates the combined signal by performing diversitycombining on signals that are equalized by each first equalization unitbased on the channel characteristic estimated by the first channelestimation unit, and outputs a combined signal to each receptionprocessing unit, and the second combining unit performs diversitycombining on signals that is equalized by each second equalization unitbased on the channel characteristic estimated by the second channelestimation unit.
 38. The reception device of claim 37, wherein the firstcombining unit further includes a hard-decision unit that performs harddecision on the combined signal according to a transmission codeposition, and outputs a hard decision result to each receptionprocessing unit.
 39. A reception device that removes an inter-carrierinterference from an OFDM signal and decodes the OFDM signal,comprising: an A/D unit operable to convert an analogue reception signalto a digital reception signal; a symbol synchronization unit operable todetermine a time window of the OFDM symbol, the time window converting atime domain signal to a frequency domain signal; a guard removal unitoperable to remove a guard interval from the OFDM symbol; a frequencydomain conversion unit operable to convert the time domain signal to thefrequency domain signal; an inter-carrier interference removal deviceoperable to remove an inter-carrier interference component from acarrier signal; a first channel estimation unit operable to estimate afirst frequency response characteristic of a channel from the carriersignal, and outputs a first channel frequency characteristic; a firstequalization unit operable to equalize the carrier signal based on thefirst channel frequency characteristic, and outputs carrier data; and adecode unit operable to perform error correction based on the carrierdata, and obtains reception bit data, the inter-carrier interferenceremoval device includes: a second channel estimation unit that estimatesa second frequency response characteristic of a channel and outputs asecond channel frequency characteristic; a second equalization unit thatequalizes the carrier signal based on the second channel frequencycharacteristic, and outputs tentative carrier data; a channel variationestimation unit that estimates a variation of the second channelfrequency characteristic, and outputs a channel variationcharacteristic; a reliability value calculation unit that calculates areliability value of the tentative carrier data; a weighting unit thatweights the tentative carrier data with use of the reliability value; aninter-carrier interference component estimation unit that estimates aninter-carrier interference component based on the weighted tentativecarrier data and the channel variation characteristic; and aninter-carrier interference removal operation unit that removes theinter-carrier interference component from the carrier signal.